Propeller drive for boats

Abstract

A double-propeller drive unit for boats, in which the under-water housing of the drive unit is designed so that the pressure center for the transverse force on the drive housing caused by water flow is located in front of the steering axis of the drive unit.

What I claim is: 
     
       1. In a propeller drive unit for boats having steering means to steer same and a pair of concentric counter-rotationally drive propeller shafts in a drive housing, each of said shafts carrying at least one propeller having a hub, said drive housing having a substantially vertical output drive shaft extending generally the length of said housing and having its lower end coupled to said pair of shafts, and a steering axis for steering said drive housing thereabout, and an anti-cavitation plate located above said propellers, the improvement wherein said drive housing comprises a forward projected surface located beneath a first plane generally horizontally defined by said anti-cavitation plate and forwardly of a second plane passing generally laterally through said first plane and through and along said steering axis, said forward projected surface being at least half but at most twice as large as a rearward projected surface of a portion of said drive housing located beneath said first plane and behind said second plane and a rearward projected surface of said hubs of said propellers thereby reducing the resultant steering torque exerted by the water flow force on said drive unit counteracting against transverse forces of said propellers whereby steering forces to be applied to said steering means is reduced. 
     
     
       2. In the propeller drive unit according to claim 1 wherein said forward projected surface is 55% of said rearward projected surfaces. 
     
     
       3. In the propeller drive unit according to claim 1 wherein said steering axis is inclined with respect to said drive shaft. 
     
     
       4. In the propeller drive unit according to claim 3 wherein said steering axis and drive shaft form an included angle which is a small acute angle.